FORT BRAGG, N.C. — The Army general at the center of a sexual-misconduct case that put the military-justice system itself on trial was spared prison Thursday and sentenced to a reprimand and a $20,000 fine — a punishment legal experts, a women’s group and members of Congress decried as shockingly light.

Brig. Gen. Jeffrey A. Sinclair, 51, immediately announced his retirement, capping a humiliating fall for the battle-tested commander once regarded as a rising star in the Army. A disciplinary board could still bust him in rank and severely reduce his pension.

The decision by the judge, Col. James Pohl, was a sweeping victory for the defense. “The system worked. I’ve always been proud of my Army,” Sinclair said outside court after reacting to his sentence with a smile and an embrace of his lawyers. “All I want to do now is go north and hug my kids and my wife.”

The former deputy commander of the storied 82nd Airborne Division was originally brought up on sexual-assault charges punishable by life in prison. He was believed to be the highest-ranking U.S. military officer ever court-martialed on such charges.

The sentence was far less than what the general faced when the case began two years ago: a possible life sentence and registration as a sex offender if he was convicted on charges that he sexually assaulted the captain, 34, who had been his lover for three years.

The judge did not explain how he arrived at a much lighter sentence, and prosecutors had no immediate comment.

Jamie Barnett, a lawyer for the captain, condemned the sentence as “a travesty” and likened it to “getting sent to the principal’s office for a stern talking to.”

“Now the Army has to face the reality that this is likely to happen again, and victims will be less likely to come forward,” he said.

The sentence, indeed the case, set off a sharp debate, including in the military, over whether the Pentagon needs to revamp the way it prosecutes sexual assault and other serious crimes, as many lawmakers contend.

“This is another sordid example of how truly broken the military-justice system is,” Rep. Jackie Speier, D-Calif., said in a statement. “This sentence is a mockery of military justice, a slap on the wrist nowhere close to being proportional to Sinclair’s offenses.”

The sentencing concluded a case that was viewed by many as embodying rampant sexual misconduct in the military, even at senior ranks, and it fueled demands by Congress that the Pentagon crack down on the problem.

But the prosecution’s case started coming apart after military lawyers concluded that their chief witness, the captain, may have lied at a hearing in January. It collapsed last week when Pohl found that political considerations may have improperly influenced the prosecution.

As a result of that finding, defense lawyers and prosecutors reached a plea agreement this week in which Sinclair pleaded guilty to lesser offenses in exchange for dismissal of the sexual-assault charges.

In addition to admitting to mistreating his mistress, he pleaded guilty to adultery, soliciting explicit pictures from female officers, disobeying a commander, possessing pornography in a combat zone and misusing his government credit card.

Also

• A military judge Thursday found a former U.S. Naval Academy football player, Joshua Tate, not guilty of sexually assaulting a fellow midshipman when she was too drunk to consent, bringing partial resolution to a highly publicized case that has lasted for nearly two years.

Col. Daniel Daugherty, the presiding judge, sent a lesser charge of making false statements back to the school, and the Naval Academy announced Thursday night that it had agreed to accept Tate’s resignation in exchange for withdrawing the lying charge.

The case stems from an off-campus party near the academy in Annapolis, Md., in 2012. The woman, then a 20-year-old sophomore, testified that she had arrived intoxicated. She said that she had no memory of parts of the evening or of having sex with Tate, and that she might have passed out.

• Air Force Tech. Sgt. Michael L. Merritt faces 25 years in military prison after he pleaded guilty this week to charges at F.E. Warren Air Force Base in Cheyenne, Wyo., that he sexually molested four girls in Germany and the United States from 2003 through 2013.